The present disclosure relates to an injection molding die used to mold a needle-equipped syringe used to inject a small amount of drug solution under the skin, and a method for producing the needle-equipped syringe using the injection molding die.
The needle-equipped syringe is a syringe in which a thin injection needle penetrates the distal end of a barrel to be used as the syringe barrel and is fixed to the barrel. A gasket is attached to the distal end of a plunger and the plunger is inserted in the barrel. This enables the needle-equipped syringe to rapidly discharge a small amount of drug solution in the barrel from the injection needle by strongly pressing the drug solution with the plunger. Thus, the needle-equipped syringe is used for hypodermic injection rather than intravenous injection. The needle-equipped syringe includes the barrel to which the injection needle is fixed. Accordingly, the needle-equipped syringe does not require a complicated operation for attaching a separate injection needle hub immediately before the administration, and allows for easy and efficient administration of the drug solution. Thus, the needle-equipped syringe is used for general purposes.
The needle-equipped syringe is produced with a manner in which a barrel including an insertion hole opening on the distal end of the barrel is produced, and an injection needle is inserted into and adhered to the insertion hole with adhesive. For pain relief during administration, a low dosage—for example, about 500 μL of a biological product such as a vaccine is administrated by hypodermic injection. The injection needle adhered to the needle-equipped syringe has a small diameter. This often raises the pressure on the plunger too high when a small amount of drug solution is administrated. This may cause the injection needle to disconnect from the distal end of the barrel.
In light of the foregoing, a needle-equipped syringe to which an injection needle is more strongly fixed (rather than adhered) has been developed. For example, as described in JP 2013-70892 A, a needle-equipped syringe in which a barrel and an injection needle provided on the distal end of the barrel are integrally formed is produced by injection molding in which resin is injected into an injection molding die on which the injection needle is provided. The needle-equipped syringe produced as describe above includes the injection needle directly and firmly fixed to the nozzle part of the barrel. Accordingly, the injection needle does not disconnect from the distal end of the barrel even when a high pressure is applied. Thus, the needle-equipped syringe is extremely safe.
A conventional injection molding die used to produce the needle-equipped syringe in injection molding, illustrated in FIG. 6, includes: a male die 10 provided with a protrusion 11 that supports the injection needle 61 so that the injection needle 61 is deeply inserted in the distal end of the core pin 13 and stands independently; and a female die 20 that forms the external surface of the barrel. A shallow insertion of the injection needle 61 into the protrusion 11 may cause an inclination of the injection needle 61 in the middle of the formation of the cavity 20a. This may causes the inclination of the central axis of the injection needle 61 of the needle-equipped syringe molded by the injection of resin after the formation with respect to the central axis of the barrel. In light of the foregoing, the protrusion 11 has a height and a thickness to some degree so that the injection needle 61 can deeply be inserted in the protrusion 11. As a result, the protrusion 11 is transferred such that a deep and wide recessed part is formed on the inner wall of the distal end of the molded barrel. The injection needle is fixed so that the proximal end of the needle is embedded in the recessed part. The recessed part is left as a “dead space.” The drug solution with which the recessed part is filled can reach no less than tens to a hundred and several tens μL. When the plunger presses the gasket, the distal end of the gasket comes into contact with the inner wall of the distal end of the barrel. This stops the plunger from pressing the gasket any more. Thus, the drug solution with which the recessed part is filled is not push out. The drug solution remains in the recessed part without discharge, and is wasted.
In light of the foregoing, in order to efficiently use a limited batch of drug solution such as seasonal flu vaccine, there is a need for producing needle-equipped syringes with a minimum dead space so that as many needle-equipped syringes as possible can be produced.